Water commonly contains organic matter, dissolved solids, and minerals that deposit scale and film (e.g., biofilm) on surfaces in drinking water distribution pipes and equipment. Quality and flow of drinking water may be deleteriously affected by such scales and films. Various cleaning and sanitizing agents may additionally leave film residues. Use of methods and compositions described herein may usefully reduce, remove, or prevent formation of these deposits.
Chlorine and chlorine-based disinfectants (including sodium hypochlorite, also known as liquid bleach) are used worldwide to reduce pathogens in drinking water. Chlorine and chlorine-based disinfectants have been widely adopted because they provide a “residual” level of protection against waterborne pathogens—namely, a low level of chlorine remaining in water after initial disinfectant application, which reduces the risk of subsequent microbial contamination after treatment. Upon initial dosing, chlorine reacts with any organic matter in water, with the amount of chlorine used in such reactions being known as the “chlorine demand” of the water. Some portion of the remaining chlorine reacts with nitrogen in water to form chloramines (with the chlorine consumed by such reactions being known as “combined chlorine”). Chloramines may also be intentionally added to water systems. Chlorine remaining in the water after chlorine demand is satisfied and combined chlorine is formed is termed “free chlorine,” which is the chlorine portion available for disinfection (e.g., to kill or incapacitate reproduction of waterborne pathogens). Chlorine residual is typically monitored at various points in drinking water distribution systems to identify points at which the residual declines or disappears—which may indicate a leak in the water distribution system or growth of bacteria.
A variable matrix of organic and inorganic deposits (variously referred to as biofilms, scale, or tuberculations) accumulates on the interior surfaces of all drinking water distribution piping systems. Control of such deposits provides advantages including improved water quality, reduced maintenance costs, and efficient use of disinfectants. Organic-laden deposits are a significant source of increased chlorine demand and can produce precursors of trihalomethanes and haloacetic acids or other disinfection byproducts. Such organic-laden deposits in drinking water systems have been shown to harbor and protect pathogenic or otherwise troublesome bacteria, viruses, algae, algal toxins, fungi, protozoa, and invertebrates. Many types of microorganisms can proliferate in these organic-laden deposits, and toxic by-products of such microorganisms can become problematic. Regardless of the level of residual disinfectant, microorganisms harbored in organic-laden deposits have been demonstrated to periodically slough off and re-entrain into flowing water, thereby contaminating other systems and exposing susceptible water consumers to biological hazards from drinking water systems (e.g., in buildings occupied by such consumers).
Many consumers are familiar with inorganic “scale” such as occurs in a teapot following the boiling of hard water. The familiar white precipitate is predominantly calcium carbonate, which deposits onto wetted surfaces of the teapot because the solubility of the salt is inversely related to temperature: as the temperature increases, the salt precipitates. In drinking water systems, however, the scaling process is more complex and the water is not boiled (it is noted that boiling water has a very destructive effect on organic compounds in water). Deposits in drinking water systems typically are not limited to just calcium carbonate or other inorganic substances, since organic materials in the water are prone to adhering to surfaces. Native organic compounds from bulk drinking water accumulate onto surfaces because adsorption is thermodynamically favored. Consequently, the deposits on surfaces in drinking water distribution systems include organic compounds in combination with inorganic compounds. The presence of organic materials give surface deposits in drinking water systems characteristics that are substantially different from inorganic scale deposits (e.g., such as may be observed on a wetted surface of a tea pot).
Primary disinfectants such as chlorine gas and liquid bleach have very limited ability to control deposits composed of both organic and inorganic constituents in drinking water systems. To the contrary, high concentration of liquid bleach in water distribution systems are typically avoided, since high concentrations have been observed to contribute to scale formation in pipes.
In order to reduce accumulation of deposits on surfaces in water distribution systems, liquid compositions including mixed oxidants or supplemental oxidants (also termed “activated sodium hypochlorite”) such as RE-Ox® scale control additive have been developed. As disclosed in U.S. Pat. No. 8,366,939 (which is commonly assigned to the same assignee of the present application, and is hereby incorporated by reference herein), liquid including supplemental oxidants may be produced by flowing salt brine solution through at least one flow electrode module comprising a center anode, a membrane surrounding the center anode, and an outer cathode surrounding the membrane, wherein at least a portion of the solution is flowed serially through an outside passage disposed between the membrane and the outer cathode, and then through an inside passage disposed between the center anode and the membrane, while electric power is applied between the anode and the cathode to electrolyze said solution, to produce a liquid desirably having a pH in a range of from about 5 to about 7.5 (with such patent also describing the product as having a “neutral pH”). The resulting composition may be supplied to water distribution systems at low concentration (e.g., from 1 to 100 ppb) to promote scale control, reduce chlorine demand, and reduce disinfection by-products.
U.S. Pat. No. 8,366,939 recognizes that a large concern in supplying activated sodium hypochlorite is shelf life, noting that degradation is caused as chlorine gas is off gassed, thereby lowering pH and lowering chlorine content. As a result, some producers of liquid compositions including supplemental oxidants have reported a shelf life of only 2 weeks, whereas the process described in U.S. Pat. No. 8,366,939 may yield a somewhat greater effective shelf life of 3 months or more. In recognition of the comparatively short shelf life of mixed oxidant solutions, certain manufacturers produce systems for on-site generation of mixed oxidants by electrolysis of a brine solution produced from water and salt.
It would be desirable to provide scale control and water treatment compositions suitable for water distribution systems with enhanced effectiveness (to provide advantages such as reduced shipping weight, reduced storage volume, and reduced size and cost of dosing equipment such as pumps and valves) in combination with extended effective shelf life; however, it is understood that increased concentration of chlorine species tends to result in faster decomposition rate (and faster loss of concentration of active ingredient), thereby inhibiting the ability to satisfy the foregoing criteria simultaneously.
Various compositions and methods disclosed herein address limitations associated with conventional compositions and methods.